1. Field
The invention relates to light beam position detection systems, and particularly to an optical assembly for providing an extremely accurate division, and subsequent detection of the position, of very small fixed or scanning spots.
2. Prior Art
During the recording process of a light beam recorder, it is essential that the scanning light spot trace a very precise line, and that any scan variations from the intended line be readily detectable. To this end, beam position detection for a straight scan line may be achieved utilizing a knife edge and directing the scanning beam half on and half off the knife edge. Such a scheme, however, suffers from noise problems, since essentially half of the beam and a proportional amount of signal is discarded. Since only one half of the beam is used, the resulting detector electronics produces additive noise rather than multiplicative noise, as in the present dual beam, balanced, detection system. Additional noise problems are caused by the intensity variations in the beam appearing as scan deviations from the straight line, i.e., from the knife edge. Futhermore, it becomes extremely difficult if not impossible to fabricate a knife edge as straight and as sharp as would be required to provide an optimized assembly of practical application for detection of the position of spots in the micron diameter range.
Other schemes are available for dividing a beam into two or more beams for purposes of tracking, multiple beam scanning, and/or intensity regulation. However, such schemes perform the beam division by optical means, whereby the geometry of the beam stays the same. That is, the beam intensity is changed without a change in the shape of the beam.
Thus, at the present time, there are no means available for providing a precise division of scanning spots having diameters in the micron range, for purposes of detecting scanning spot deviations, or for determining the position of a small fixed spot at the entrance to a split optical lens.